The present invention relates to an internal intermediate pressure type two-stage compression rotary compressor, and more particularly to an internal intermediate pressure type two-stage rotary compressor, for example, which can reduce a pressure change at a time of starting and can reduce a weight of a pressure vessel.
In conventional, in a two-cylinder type two-state compression rotary compressor in which an electrically driven element and two rotary compression elements are arranged and received within a sealed vessel, the sealed vessel is used as an internal low pressure type of an internal, intermediate pressure type.
In the case of the internal low pressure type, a refrigerant gas having a low temperature and a low pressure and returning to an inner portion of the sealed vessel from an external refrigerant circuit constituting a refrigerant cycle via an accumulator is sucked from a suction passage so as to be compressed at a first stage by a first rotary compression element, and is thereafter fed out to an intermediate cooling device positioned at an external portion, thereafter the refrigerant gas having an intermediate pressure is directly sucked to a second rotary compression element by a refrigerant pipe and is further compressed at a second stage, and the refrigerant gas having a high temperature and a high pressure is fed out to the external refrigerant circuit mentioned above by the refrigerant pipe.
On the contrary, in the case of the internal intermediate pressure type, the refrigerant gas having the low temperature and the low pressure and returning from the external refrigerant circuit constituting the refrigerant cycle via the accumulator is directly sucked to the first rotary compression element by the refrigerant pipe, and is compressed here so as to be discharged within the sealed vessel. Next, the discharged refrigerant gas having the intermediate pressure is compressed by the second rotary compression element so as to be fed out as the refrigerant gas having the high temperature and the high pressure to the external refrigerant circuit. That is, the pressure of the refrigerant gas discharged within the sealed vessel becomes the intermediate pressure between the first stage suction pressure and the second stage discharge pressure. Then, the intermediate pressure is determined on the basis of a bearing load, work loads in the respective stages, and the like.
However, in the case that the intermediate pressure is lower than a pressure (an equilibrium pressure) at a time when the compressor stops, a difference between the high pressure and the low pressure is lost and the, pressure within the compressor becomes an equilibrium state, the pressure within the sealed vessel is rapidly reduced at a time of starting the compressor, the refrigerant lying up in the oil together therewith becomes bubbles and an oil foaming is generated. Further, in the case that the intermediate pressure is higher than the equilibrium pressure, at a time when the compressor stops, the refrigerant gas running into the oil after starting becomes bubbles due to an increase of temperature of the sealed vessel, whereby the oil foaming is generated. Further, in the case of using a CO2 refrigerant, the refrigerant pressure reaches 100 kg/cm2G in a high pressure side, and 30kg/cm2G in a low pressure side, and an amount of oil flowing out to the low pressure side due to the pressure difference is increased. Further, it is necessary to apply any higher withstand pressure design among that against the intermediate pressure and that against the equilibrium pressure to the sealed vessel.
Accordingly, a main object of the present invention is to provide an internal intermediate pressure type two-stage compression rotary compressor which can reduce a pressure change at a time of starting or the like, can easily employ a withstand pressure design of a sealed vessel and can reduce a weight of the pressure vessel.
In accordance with the present invention, there is provided an internal intermediate pressure type two-stage compression rotary compressor comprising, an electrically driven element provided within a sealed vessel, first and second rotary compression elements driven by the electrically driven element, CO2 refrigerant gas compressed at a first stage by the first rotary compression element, being discharged within the sealed vessel and the discharged refrigerant gas having an intermediate pressure, being compressed at a second stage by the second rotary compression element,
wherein a ratio of volume between the rotary compression element at the first stage and the rotary compression element at the second stage is set so that the equilibrium pressure becomes equal to the intermediate pressure.
The pressure change at a time of starting becomes small by setting the ratio of volume of the rotary compression elements executing the first and second stages of compression to a range between 1:0.5 and 1:0.8, whereby it is possible to restrict the oil foaming from being generated. Further, the withstand pressure design standard becomes 7000 kPa which is substantially equal to the equilibrium pressure, and becomes a value equal to that of the internal low pressure type.